Title:  Direct Aperture IMRT Optimization: an Exact Approach

Traditionally, Intensity Modulated Radiation Therapy (IMRT) cancer treatment planning has been performed in two phases: a first phase, called fluence map optimization, in which optimal beamlet intensities are determined, followed by a second, leaf sequencing, phase in which these fluence maps are decomposed into deliverable apertures and corresponding intensities. Most approaches that integrate these two phases by simultaneously identifying high quality apertures and intensities are heuristic in nature, mainly due to the astronomical number of available apertures. We instead formulate an integrated model that is exact in the case where only convex treatment plan evaluation criteria are considered. We find empirically that this approach yields high-quality treatment plans with only a relatively small number of apertures. Moreover, this approach lends itself very well to incorporating delivery aspects that cannot be incorporated in a beamlet-based fluence map optimization approach.